Abstract
<h2>Summary</h2> Design criteria for dysprosium(III) single-molecule magnets (SMMs) with large thermal energy barriers to magnetic reversal have been established and proven, and the challenge to enhance performance is in understanding and controlling electron-vibration coupling that is the origin of magnetic reversal. We have prepared an SMM, [Dy(L)<sub>2</sub>(py)<sub>5</sub>][BPh<sub>4</sub>] <b>1</b> (HL = (S)-(-)-1-phenylethanol), based on the archetype [Dy(O<sup>t</sup>Bu)<sub>2</sub>(py)<sub>5</sub>][BPh<sub>4</sub>] <b>2</b>. Compounds <b>1</b> and <b>2</b> have similarly large energy barriers of <i>U</i><sub>eff</sub> = 1,130(20) cm<sup>−1</sup> and <i>U</i><sub>eff</sub> = 1,250(10) cm<sup>−1</sup>, and yet <b>1</b> shows magnetic hysteresis at a far higher temperature of 22 K <i>cf</i>. <i>T</i><sub>H</sub> = 4 K for <b>2</b>. <i>Ab initio</i> calculation of the electron-vibration coupling and spin dynamics shows that substitution of the alkoxide ligand in fact enhances relaxation over the energy barrier for <b>1</b> compared with <b>2</b>, in agreement with experiment, and that the higher temperature of magnetic hysteresis likely owes to reduced quantum tunneling at low temperatures.
Highlights
Single-molecule magnets (SMMs) have received a lot of attention from physicists and chemists alike in the past few decades[1,2,3,4,5,6,7,8,9] because of their potential applications in information storage, spintronics, and quantum information.[10,11,12,13] There have been major breakthroughs in the last few years, including vast increases in the energy barrier for reversal of magnetization (Ueff)
The question is, why in some cases a high Ueff value is accompanied by open magnetic hysteresis at 80 K19 and in other cases there can be almost no hysteresis despite a large Ueff value.[21]
Relaxation by quantum tunneling of the magnetization (QTM) at the lowest temperatures is enabled by the off-axial crystal field (CF) terms or by the confluence of a transverse CF and small magnetic fields and does not involve an exchange of phonons; we have recently shown that there might be a connection to molecular flexibility and vibrational motion.[22,26]
Summary
Single-molecule magnets (SMMs) have received a lot of attention from physicists and chemists alike in the past few decades[1,2,3,4,5,6,7,8,9] because of their potential applications in information storage, spintronics, and quantum information.[10,11,12,13] There have been major breakthroughs in the last few years, including vast increases in the energy barrier for reversal of magnetization (Ueff) In most cases, this was achieved by targeting axial ligand fields with strong donor atoms[14,15,16,17,18,19] but was obtained for endofullerenes.[20] very high Ueff values >700 cmÀ1 are not on their own sufficient to increase the maximum temperature at which magnetic information can be retained. The question is, why in some cases a high Ueff value is accompanied by open magnetic hysteresis at 80 K19 and in other cases there can be almost no hysteresis despite a large Ueff value.[21]
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